Light weight implementations of real-time communication protocols and applications in Python
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README.md

Light weight implementations of real-time communication protocols and applications in Python

rtclite

This project aims to create an open source repository of light weight implementations of real-time communication (RTC) protocols and applications. In a nutshell, it contains reference implementations, prototypes and sample applications, mostly written in Python, of various RTC standards defined in the IETF, W3C and elsewhere, e.g., RFC 3261 (SIP), RFC 3550 (RTP), RFC 3920 (XMPP), RTMP, etc.

Background

This project was migrated from https://code.google.com/p/rtclite on May 17, 2015
Keywords: Python, Realtime, Communication, Library, Academic, SIP, RTP, WebRTC, RTMP
Members: kundan10, theintencity, mamtasingh05, voipresearcher
Links: Project, Support
License: GNU Lesser GPL

The "rtclite" project is created to host the source code of the "39 peers" project, and the two project names are used interchangeably here. Please visit the project website for further details.

This project is an effort to unify my Python-based projects related to SIP, RTP, RTMP, Web into a single theme of real-time communication (RTC). In particular, the initial source code is borrowed after cleanup from these projects, without adding any significant new functionality:

p2p-sip: SIP, P2P, XMPP and other related code. rtmplite: RTMP, RTMFP and SIP-RTMP translation. restlite: REST web APIs

Motivation

The primary motivation is described in my earlier blog article, a proposal for reference implementation repositiory for RFCs.

With growing number of emerging RTC standards, the trend of creating specifications without implementations, and consecutively the interoperability problems have increased. This project will hopefully simplify the job of an RTC programmer and, in the long term, will result in more interoperable and robust RTC products. This project contains source code of various RTC specifications. The source code is annotated with text snippets from the relevant specification to show (a) how the code fragment implements the specification, (b) which part of the specification is relevant to the code fragment, and vice-versa, and (c) the implicit code documentation borrowed from the text in the specification.

Click to browse the annotated source code.

Alternatively, click on individual modules below to view that annotated code and its Python source lines of code (SLoC). The SLoC also shows the concise nature of this Python implementation of various protocols and applications.

Module Package or Description SLoC
package: rtclite.std.ietf
rfc1035 DNS lookup for any record type 1125
rfc2198 RTP payload type for redundant audio data 51
rfc2396 Various forms of addresses such as URI or SIP address 177
rfc2617 HTTP basic and digest authentication 92
rfc2833 DTMF touch-tone payload in RTP packet 48
rfc3261 Session Initiation Protocol (SIP) 1425
rfc3263 SIP server discovery using DNS NAPTR, SRC and A records 107
rfc3264 SDP offer-answer model for unicast session in SIP 97
rfc3489 Basic NAT traversal technologies such as STUN, NAT discovery using STUN and TURN 595
rfc3550 Real-time Transport Protocol (RTP) and companion control protocol RTCP 725
rfc3551 Static payload types for RTP 34
rfc3920 XMPP core for client side 351
rfc3921 IM and presence of XMPP client side 290
rfc4566 Session Description Protocol (SDP) 148
rfc5389 Session traversal utilities for NAT (STUN) 128
rfc6455 WebSocket protocol - client and server 565
rfc7064 URI scheme for STUN, patch rfc2396 28
rfc7065 URI scheme for TURN, patch rfc2396 41
package: rtclite.std.itu_t
t140 real-time text (RTT) payload in RTP 13
package: rtclite.std.w3c
simplexml Simple XML DOM with Pythonic convenient methods and operators for XML and XMLList 363
package: rtclite.app.sip
client SIP user agent library for registration, call, IM, conferences 1258
server Very simple SIP registration, proxy server, including WebSocket 100
caller command line SIP caller and call listener with voice, TTS, ASR, DTMF 729
api SIP API for use in programmable servers and clients 371
p2p One way to implement P2P-SIP, not based on the IETF standard 315
package: rtclite.app.net.p2p
dht Distributed Hash Table (DHT) inspired by BambooDHT and OpenDHT 1712
dhtgui GUI to see P2P network in action 356
opendht (defunct) Interface to connect to OpenDHT 63
pipe P2P pipe abstraction 590
package: rtclite.app.sec
crypto Crypto library wrapper, e.g., PKI, ASN1, ARC, etc. 251
dummycrypto Stub for crypto module 24
package: rtclite.app.web.rest
base Building blocks for creating REST APIs 196
data Expose structured data as REST resources 152
files Expose local file structure as REST resources 94
package: rtclite.app.web.rtc
notify WebRTC notification server for signaling over WebSocket 198
package: rtclite.vnd.adobe
rtmp Real Time Messaging Protocol (RTMP) parsing, formatting, server, and FLV 1068
rtmpclient command line RTMP client 345
rtmpt RTMP tunneling 165
siprtmp SIP-RTMP translation for voice and video 1147
aes Pure python based AES, used only when PyOpenSSL is not found 179
amf Action Message Format (AMF) 0 and 3 367
rtmfp Real-Time Media Flow Protocol (RTMFP) parsing and formatting 2095
package: rtclite.vnd.google
chat Send and receive Google Chat messages over XMPP 60
package: rtclite
common Common utility methods and classes 410
multitask Co-operative multitasking 469

Furthermore, the project contains various applications built on top of these open standards and open source implementations to demonstrate real use cases, e.g., SIP proxy server, XMPP client, command line SIP dialer, SIP-RTMP gateway, etc. The light-weight nature of the various Python modules enables other developers to easily use these in their projects, without other complex framework dependencies.

Design Goals

The primary design goal of this project is to provide reference implementation of popular real-time communication protocols. The implementation is done in Python 2.7 programming language, but may be ported in future to others. There are two parts in the source code -- the protocols and the applications. Following goals are met in the current implementations of the protocols.

  • System Portability: apart from the Python standard library, the project should not rely on other third-party libraries. If such third- party libraries become necessary, consider including them in the repository or provide clear instructions for such dependency. The module should isolate such dependencies to smaller part if possible. The project should therefore be portable to many interpreters and runtime environments.
  • Threading: threading vs event-driven programming style is decision that best left to the application developer instead of forcing a particular choice in the library. The project should not impose such decision in reference implementation. If it is necessary to include such choice, then it should provide reasonable set of alternatives pre-built in the module.
  • Concise and Precise Code: Python enables expressing ideas in code in less number of lines. The programmer should further honor the Pythonic programming style. Less number of lines means that one can write software faster, and with less garbage (syntactic sugar), one can read and understand the code easily. Moreover, testing and review efforts are less. The resulting improvement in programmer's efficiency reflects in her motivation to write more clean code.
  • Testing: testing is an integral part of all code in this project. It uses doctest whereever possible to integrate code with documentation and testing. Alternatively, dedicated test and sample applications are included for manual or automated testing. Generally, running a protocol module on command line via Python interpreter should run its test cases and report any errors.
  • Logging: standard logging module is used at various log levels. The code should avoid using the standard print statements as much as possible for logging - helps in migrating to Python3 in future, and reduces unwanted output when the module is included elsewhere.

On the other hand, implementation of an application may depend on the specific system, e.g., for audio/video interface, or specific threading vs. event programming style, or custom user interface, e.g., web vs. curses vs. command line. These applications are for demonstration purpose, and not for production use.

Software Structure

The std, app and vnd packages under top-level rtclite include the implementations of the protocols and the applications. The std package further includes sub-packages for standard bodies, e.g., ietf and w3c. The app package contains not only the applications but also supporting library modules classified under high level categories such as net, sip or sec, and the vnd package contains vendor specific protocol implementations such as adobe sub-package for rtmp and siprtmp.

In an application, a module from this project should always be imported with the package hierarchy, e.g.,

import rfc3261 # WRONG
from rtclite.std.ietf import rfc3261 # RIGHT
from rtclite.std.ietf.rfc3261 import UserAgent # RIGHT AGAIN
import rtclite.std.ietf.rfc3261 # STILL RIGHT

Similarly, a protocol or application module should be invoked with the right package hierarchy, e.g.,

cd rtclite/std/ietf; python rfc3921.py  # WRONG
python -m rtclite.std.ietf.rfc3921 # RIGHT

The included Makefile can be used on Unix-like systems to test all the protocol modules, to generate annotated source file documentations, and to create installable distribution.

make test
make doc

License and contributions

Please see LICENSE for details on software license and copyright. In particular, this software is available as either LGPL or alternative license. Any other contributors, who submit code or patches to this project automatically transfer the copyright of their work to the original author. This allows the original author to create derivative work or issue alternative license outside of LGPL.